I am pretty sure he wrote "ZAC" underneath the signature. He does sometimes write "ZAC" or "ZE" underneath his signature, here's an example:
He wrote "ZE" there, and below is an example where he signed "ZAC E___":
It's the same writing as in the scan you posted! So I think this one looks authentic to me. Just very squashed together and rushed, but you said it's in person, so that would make sense!